This invention relates to a process of producing an image of a scene (field), and preferably a heat image, in which the scene to be observed is optically focused, analyzed linewise by a mechanically moved scanning device (scanner), and fed over a multi-element detector, the elements of which are arrayed in a row perpendicular to the scanning motion of the scanner, the video signals of the detector being fed via an amplifier to an image-presentation or display device. Aside from the process, the invention also covers an apparatus for the carrying out of the process.
In known devices for the production of heat images, as shown for example in U.S. Pat. No. 3,742,238, a plurality of rectangular detector elements are arrayed on a single crystal, spaced in a row one after the other, the distance between them corresponding to their individual length dimension, and their center lines being aligned in the direction of the row. Such a detector array provides a first dimensional component of an analysis of an image. The second dimension for analysis of the image is in the direction perpendicular to the detector row and is as a rule effected by a mechanically moved scanning device, a so-called scanner. The scanning device sweeps the observed scene over the detector in the direction perpendicular to the detector row. The scanner may consist of elements which oscillate back and forth, and which are used for scanning during both the forward and backward displacements of the oscillation.
Such a scanner is known in which an oscillating mirror sweeps the image of the scene over the detector row, as described, for instance, in German Gebrauchsmuster No. 7,217,873. By a slight tilting of the mirror in the direction of the detector row in each case at the end points of the main scanning motion, the result is obtained that the scene points which are focused, for instance, onto detector-element spacings during forward travel of the mirror are focused onto the detector elements themselves during return travel of the mirror, thus interlacing elements of the field sweep on forward travel, with elements of the field sweep on return travel. The image-presentation or display device consists in known devices of a row of light-emitting diodes, arrayed similarly to the detector array. Such a diode presentation is viewed, for instance, directly by means of an ocular, or is focused by means of an objective onto the cathode of an opto-electronic transducer, the display-ray path being folded, in each case, at the same oscillating mirror as effects the scanning of the scene.
The front side of the oscillating mirror is frequently used for scanning with the detector array, the rear side of the mirror being used for the reproduction or display.
In known processes and apparatus for the production of heat images, detector, amplifier and light-emitting diodes have only a limited electrical bandwidth. In order to improve the signal-to-noise ratio, the inherent bandwidth of the amplifier is generally additionally limited. As a result, a low-pass filtering action takes place in the image transmission. As a result of this, signal jumps which are produced by objects having sharp edges are transmitted at a finite rise rate or speed. A phase error results by which, for instance, the centroids of thin structures of the scene are delayed in time in the image, i.e., in the case of scanning of the lines in the direction from left to right, they are reproduced with a phase delay which presents the displayed appearance of a shift towards the right. If the scanning device is used in both forward and return directions of travel, the phase error upon the backward or return travel causes apparent shift to the left. Linear structures of the scene which are perpendicular to the scanning device are therefore reproduced in a degraded form, characterized by oppositely staggered interlaced offsets of given features of the field. As a result, the power of resolution of the apparatus is decreased.